1. Field of the Disclosure
Embodiments disclosed herein relate generally to blowout preventers used in the oil and gas industry. Specifically, embodiments relate to methods of curing and manufacturing seals for use in blowout preventers, in which the seals may include elastomeric and rigid materials.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well, for example, safety devices must be put in place to prevent injury to personnel and damage to equipment resulting from unexpected events associated with the drilling activities.
Drilling wells involves penetrating a variety of subsurface geologic structures, or “layers.” Occasionally, a wellbore will penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with a kick is generally produced by an influx of formation fluids, which may be a liquid, a gas, or a combination thereof, into the wellbore. The pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high-pressure region to a low-pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. Such “blowouts” may result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and substantial injury or death of rig personnel.
Because of the risk of blowouts, devices known as blowout preventers are installed above the wellhead at the surface or on the sea floor in deep water drilling arrangements to effectively seal a wellbore until active measures can be taken to control the kick. Blowout preventers may be activated so that kicks are adequately controlled and “circulated out” of the system. There are several types of blowout preventers, the most common of which are annular blowout preventers (including spherical blowout preventers) and ram blowout preventers. Each of these types of blowout preventers will be discussed in more detail.
Annular blowout preventers typically use large annular, rubber or elastomeric seals having metal inserts, which are referred to as “packing units.” The packing units may be activated within a blowout preventer to encapsulate drillpipe and well tools to completely seal an “annulus” between the pipe or tool and a wellbore. In situations where no drillpipe or well tools are present within the bore of the packing unit, the packing unit may be compressed such that its bore is entirely closed. As such, a completely closed annular blowout preventer packing unit acts like a shutoff valve. Typically, the packing unit may be quickly compressed, either manually or by machine, to result in a seal thereabout and to prevent well pressure from causing a blowout.
An example of an annular blowout preventer having a packing unit is disclosed in U.S. Pat. No. 2,609,836, issued to Knox, assigned to the assignee of the present disclosure, and incorporated herein by reference in its entirety. The packing unit of Knox includes a plurality of metal inserts embedded in an elastomeric body, in which the metal inserts are completely bonded with the elastomeric body. The metal inserts are spaced apart in radial planes in a generally circular fashion extending from a central axis of the packing unit and the wellbore. The inserts provide structural support for the elastomeric body when the packing unit is radially compressed to seal against the well pressure. Upon compression of the packing unit about a drillpipe or upon itself, the elastomeric body is squeezed radially inward, causing the metal inserts to move radially inward as well.
Referring now to FIG. 1, an annular blowout preventer 101 including a housing 102 is shown. Annular blowout preventer 101 has a bore 120 extending therethrough corresponding with a wellbore 103. A packing unit 105 is then disposed within annular blowout preventer 101 about bore 120 and wellbore 103, Packing unit 105 includes an elastomeric annular body 107 and a plurality of metal inserts 109. Metal inserts 109 are disposed within elastomeric annular body 107 of packing unit 105, which are distributed in a generally circular fashion and spaced apart in radial planes extending from wellbore 103. Further, packing unit 105 includes a bore 111 concentric with bore 120 of blowout preventer 101.
Annular blowout preventer 101 is actuated by fluid pumped into opening 113 of a piston chamber 112. The fluid applies pressure to a piston 117, moving piston 117 upward and translating force to packing unit 105 through a wedge face 118. The force translated to packing unit 105 from wedge face 118 is directed upward toward a removable head 119 of annular blowout preventer 101, and inward toward a central axis of wellbore 103 of annular blowout preventer 101. Because packing unit 105 is retained against removable head 119 of annular blowout preventer 101, packing unit 105 does not displace upward from the force translated to packing unit 105 from piston 117. However, packing unit 105 does displace inward from the translated force, which compresses packing unit 105 toward central axis of wellbore 103 of the annular blowout preventer 101. In the event drillpipe is located within bore 120, with sufficient radial compression, packing unit 105 will seal about the drillpipe into a “closed position.” The closed position is shown in FIG. 5. In the event a drillpipe is not present, packing unit 105, with sufficient radial compression, will completely seal bore 111.
Annular blowout preventer 101 goes through an analogous reverse movement when fluid is pumped into opening 115 of piston chamber 112. The fluid translates downward force to piston 117, such that wedge face 118 of piston 117 allows the packing unit 105 to radially expand to an “open position.” The open position is shown in FIG. 4. Further, removable head 119 of annular blowout preventer 101 enables access to packing unit 105 such that packing unit 105 may be serviced or changed if necessary.
Referring now to FIGS. 2, 3A, and 3B together, packing unit 105 and metal inserts 109 used in annular blowout preventer 101 are shown in more detail. In FIG. 2, packing unit 105 includes an elastomeric annular body 107 and a plurality of metal inserts 109. Metal inserts 109 are distributed in a generally circular fashion and spaced apart in radial planes within elastomeric annular body 107. FIGS. 3A and 3B show examples of metal inserts 109 that may be disposed and embedded within elastomeric annular body 107. Typically, metal inserts 109 are embedded and completely bonded to elastomeric annular body 107 to provide a structural support for packing unit 105. The bond between annular body 107 and metal inserts 109 restrict relative movement elastomer within the elastomeric annular body 107. More discussion of the bonds between elastomeric bodies and metal inserts within a packing unit may be found in U.S. Pat. No. 5,851,013, issued to Simons, assigned to the assignee of the present disclosure, and incorporated herein by reference in its entirety.
Referring now to FIGS. 4 and 5, examples of packing unit 105 in the open position (FIG. 4) and closed position (FIG. 5) are shown. When in the open position, packing unit 105 is relaxed and not compressed to seal about drillpipe 151 such that a gap is formed therebetween, allowing fluids to pass through the annulus. As shown in FIG. 5, when in the closed position, packing unit 105 is compressed to seal about drillpipe 151, such that fluids are not allowed to pass through the annulus. In this manner, the blowout preventer may close the packing unit 105 to seal against wellbore pressure from the blowout originating below.
Similarly, spherical blowout preventers use large, semi-spherical, elastomeric seals having metal inserts as packing units. Referring to FIG. 6, an example of a spherical blowout preventer 301 disposed about a wellbore axis 103 is shown. FIG. 6 is taken from U.S. Pat. No. 3,667,721 (issued to Vujasinovic and incorporated by reference in its entirety). Spherical blowout preventer 301 includes a lower housing 303 and an upper housing 304 releasably fastened together with a plurality of bolts 311, wherein housing members 303, 304 may have a curved, semi-spherical inner surface. A packing unit 305 is disposed within spherical blowout preventer 301 and typically includes a curved, elastomeric annular body 307 and a plurality of curved metal inserts 309 corresponding to the curved, semi-spherical inner surface of housing members 303, 304. Metal inserts 309 are thus disposed within annular body 307 in a generally circular fashion and spaced apart in radial planes extending from a central axis of wellbore 103.
Additionally, ram blowout preventers may also include elastomeric seals having metal inserts. The large seals are typically disposed on top of ram blocks or on a leading edge of ram blocks to provide a seal therebetween. Referring now to FIG. 7, a ram blowout preventer 701 including a housing 703, a ram block 705, and a top seal 711 is shown. With respect to FIG. 7, only one ram block 705 is shown; typically, though, two corresponding ram blocks 705 are located on opposite sides of a wellbore 103 from each other (shown in FIG. 8). Ram blowout preventer 701 includes a bore 720 extending therethrough, bonnets 707 secured to housing 703 and piston actuated rods 709, and is disposed about central axis of a wellbore 103. Rods 709 are connected to ram blocks 705 and may be actuated to displace inwards towards wellbore 103. Rams blocks 705 may be pipe rams, variable bore rams, shear rams, or blind rams. Pipe and variable bore rams, when activated, move to engage and surround drillpipe and/or well tools to seal the wellbore. In contrast, shear rams engage and physically shear any wireline, drillpipe, and/or well tools in wellbore 103, whereas blind rams close wellbore 103 when no obstructions are present. More discussion of ram blowout preventers may be found in U.S. Pat. No. 6,554,247, issued to Berekenhoff, assigned to the assignee of the present disclosure, and incorporated herein by reference in its entirety.
Referring now to FIG. 8, ram blocks 705A, 705B and top seals 711A, 711B used in ram blowout preventer 701 are shown in more detail. As shown, top seals 711A, 711B are disposed within grooves 713 of ram blocks 705A, 705B, respectively, and seal between the top of ram blocks 705 and housing 703 (shown in FIG. 7). As depicted, ram block 705A is an upper shear ram block having top seal 705A, and ram block 705B is a lower shear ram block having top seal 705B. When activated, ram blocks 705A, 705B move to engage, in which shears 715A engage above shears 715B to physically shear drillpipe 151. As ram blocks 705A, 705B move, top seals 705A, 705B seal against housing 703 to prevent any pressure or flow leaking between housing 703 and ram blocks 705A, 705B.
Referring now to FIGS. 9A and 9B, top seals 711A, 711B are shown in more detail. As shown particularly in FIG. 9A, top seals 711A, 711B comprise an elastomeric band 751, elastomeric segments 753 attached at each end of elastomeric band 751, and a metal insert 755 disposed within each elastomeric segment 753. Top seal 705A for ram block 705A (i.e., the upper shear ram block) may also include a support structure 757 connected between elastomeric segments 753. As shown in a cross-sectional view in FIG. 9B, metal insert 755 disposed within elastomeric segment 753 has an H-shaped cross-section. The H-shaped cross-section of metal insert 755 should be understood that top seals 711A, 711B may be used with either pipe rams, blind rams, or shear rams (shown in FIG. 8).
Referring now to FIG. 10, a ram block 705A with a top seal and a ram packer 717A used in ram blowout preventer (e.g., 701 of FIG. 7) is shown. FIG. 10 is taken from U.S. Patent Application Publication No. 20040066003 (issued to Griffin et al. and incorporated herein by reference in its entirety). Instead of a shear rams (shown in FIGS. 7 and 8), FIG. 10 depicts a pipe ram assembly having a variable bore ram packer 717A comprised of elastomer and metal. As shown, variable bore ram packer 717A comprises an elastomeric body 761 of a semi-elliptical shape having metal packer inserts 763 molded in elastomeric body 761. Metal packer inserts 763 are arranged around a bore 765 of elastomeric body 761. As mentioned above with respect to pipe rams or variable bore rams, when activated, ram packer 717A (along with a corresponding ram packer oppositely located from ram packer 717A) moves to engage and surround drillpipe and/or well tools located in bore 765 to seal the wellbore.
For any seal mechanism comprising elastomers and metal in blowout preventers (e.g., packing units in the annular and spherical blowout preventers and top seals and ram packers in the ram blowout preventer), loads may be applied to contain pressures between various elements of the blowout preventers. For example, with respect to the annular blowout preventer shown in FIG. 1, as the fluid force is translated from piston 117 and wedge face 118 to packing unit 105 to close packing unit 105 towards central axis of wellbore 103, the fluid force generates stress and strain within packing unit 105 at areas and volumes thereof contacting sealing surfaces (e.g., wedge face 117 and drillpipe 151) to seal against wellbore pressure from below. The stress occurring in packing unit 105 is roughly proportional to the fluid force translated to packing unit 105.
As stress is incurred by blowout preventer seals, the material of the seals will strain to accommodate the stress and provide sealing engagement. The amount of strain occurring in the material of the seal is dependent on a modulus of elasticity of the material. The modulus of elasticity is a measure of the ratio between stress and strain and may be described as a material's tendency to deform when force or pressure is applied thereto. For example, a material with a high modulus of elasticity will undergo less strain than a material with a low modulus of elasticity for any given stress. Of the materials used in blowout preventer seals, the metal inserts have substantially larger moduli of elasticity than the elastomeric portions. For example, the modulus of elasticity for steel (typically about 30,000,000 psi; 200 GPa) is approximately 20,000-30,000 times larger than the moduli of elasticity for most elastomers (typically about 1,500 psi; 0.01 GPa).
Historically, when examining, designing, and manufacturing seals for blowout preventers, such as packing units for blowout preventers, the locations and amounts of stress and/or strain (i.e., stress concentrations, strain concentrations) occurring within the seal have been the largest concern and received the most attention and analysis. As the seal is subject to loads (e.g., repetitive and cyclic closures of a packing unit of an annular blowout preventer about a drillpipe or about itself), the magnitude and directions of the stresses and strains occurring across the seat are evaluated to determine the performance of the seal. A common technique used for this evaluation is finite element analysis (“FEA”). Specifically, FEA may be used to simulate and evaluate the stress and/or strain concentrations which occur across the seal under given displacement conditions.
When designing and manufacturing high strain elastomeric seals containing rigid inserts, there may be a significant discrepancy between the theoretical stress and strain predicted by FEA and actual stress and strain. Thus, current modeling and analysis techniques for blowout preventer seals may not provide adequate information to improve their design and manufacture.
Additionally, performance of a manufactured seal may also depend upon the properties of the elastomeric material used. Properties of the elastomeric material depend not only on the base material (elastomer) properties, but also on the degree of curing, or degree of crosslinking, of the elastomeric material obtained during seal manufacture. For example, excessively cured or crosslinked elastomeric material may be rigid and not function properly; i.e., curing may affect the modulus of elasticity of the elastomeric material. Under-cured elastomeric material may lack resiliency.
Accordingly, there exists a need for methods to improve the design, manufacture, and curing processes for blowout preventer seals.